Well it's been a while since this question was asked, but here's another, perhaps easier way to get this. Use the built-in measure tool. Open the tool, click on the little globe icon. (The measure tool also measures along a line (ruler) and will allow you to trace a polygon.) Click on your map. The coordinates where you clicked will appear in the add in box.
The values that are returned are in the same units as you've set for your display. You'll get MGRS info if that's the coordinate system you have set for Display. If you wish to save the results, select Add to Map.